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TLS

TLS. 14.1 Introduction 14.2 TLS Record Protocol 14.3 TLS Handshake Protocol 14.4 Summary. 14.1 Introduction. Transport Layer Security (TLS) [RFC2246] TLS provides transport layer security for Internet applications

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TLS

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  1. TLS

  2. 14.1 Introduction 14.2 TLS Record Protocol 14.3 TLS Handshake Protocol 14.4 Summary

  3. 14.1 Introduction • Transport Layer Security (TLS) [RFC2246] • TLS provides transport layer security for Internet applications • It provides for confidentiality and data integrity over a connection between two end points • TLS operates on a reliable transport, such as TCP, and is itself layered into • TLS Record Protocol • TLS Handshake Protocol

  4. Advantage of TLS • applications can use it transparently to securely communicate with each other • TLS is visible to applications, making them aware of the cipher suites and authentication certificates negotiated during the set-up phases of a TLS session

  5. 14.2 TLS Record Protocol • TLS Record Protocol layers on top of a reliable connection-oriented transport, such as TCP • TLS Record Protocol • provides data confidentiality using symmetric key cryptography • provides data integrity using a keyed message authentication checksum (MAC) • The keys are generated uniquely for each session based on the security parameters agreed during the TLS handshake

  6. Basic operation of the TLS Record Protocol • read messages for transmit • fragment messages into manageable chunks of data • compress the data, if compression is required and enabled • calculate a MAC • encrypt the data • transmit the resulting data to the peer

  7. At the opposite end of the TLS connection, the basic operation of the sender is replicated, but in the reverse order • read received data from the peer • decrypt the data • verify the MAC • decompress the data, if compression is required and enabled • reassemble the message fragments • deliver the message to upper protocol layers

  8. 14.3 TLS Handshake Protocol • TLS Handshake Protocol is layered on top of the TLS Record Protocol • TLS Handshake Protocol is used to • authenticate the client and the server • exchange cryptographic keys • negotiate the used encryption and data integrity algorithms before the applications start to communicate with each other

  9. Figure 14.1 illustrates the actual handshake message flow • [Step1] • the client and server exchange Hello messages • the client sends a ClientHello message, which is followed by the server sending a ServerHello message

  10. these two messages establish the TLS protocol version, the compression mechanism used, the cipher suite used, and possibly the TLS session ID • additionally, both a random client nonce and a random server nonce are exchanged that are used in the handshake later on

  11. [Step2] • the server may send any messages associated with the ServerHello • depending on the selected cipher suite, it will send its certificate for authentication • the server may also send a key exchange message and a certificate request message to the client, depending on the selected cipher suite

  12. to mark the end of the ServerHello and the Hello message exchange, the server sends a ServerHelloDone message

  13. [Step3] • next, if requested, the client will send its certificate to the server • in any case, the client will then send a key exchange message that sets the pre-master secret between the client and the server • optionally, the client may also send a Certificate Verify message to explicitly verify the certificate that the server requested

  14. [Step4] • then, both the client and the server send the ChangeCipherSpec messages and enable the newly negotiated cipher spec • the first message passed in each direction using the new algorithms, keys and secrets is the Finished message, which includes a digest of all the handshake messages • each end inspects the Finished message to verify that the handshake was not tampered with

  15. 註： • Digest of all the handshake messages • means the results of applying a one-way hash function to the handshake messages

  16. 14.4 Summary • TLS protocol provides transport layer security for Internet applications and confidentiality using symmetric key cryptography and data integrity using a keyed MAC • It also includes functionality for client and server authentication using public key cryptography

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